coastal and marine natural values of the kimberley - wwf - Australia

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14. Coastal and Marine Natural Values of the Kimberley2.THE KIMBERLEY2.1 OVERVIEWThe Kimberley is characterised byextremely low human populationdensity and lack of infrastructure.Dampierland and the Northern Kimberleyare particularly remote with an almostcomplete absence of roads reaching thecoast. Islands are the predominant coastalformation with thousands distributedbetween Broome and Cape Londonderry.There are over 200 islands in theBonaparte and Buccaneer Archipelagosalone. Islands are particularly importantas a microcosm of the Mitchell Plateauenvironment and a refuge for intactecosystems and species otherwisethreatened on the mainland (Burbidge etal., 1991; How et al., 2006). They are alsoimportant breeding grounds for marineturtles and seabirds.The coastal component consists of manyestuaries, inlets and embayments withmangrove, tidal sediment flats, channels,seagrass beds, islands, shoals, rocky reef,coral reef and muddy seabed habitats.The shelf extends approximately 370km offshore (depths of 20-200 m) andhas a high diversity of habitats andgeomorphic features. These includegravel and sandy plains, some withsponge and coral gardens, which gradeinto muddy substrata near and on theslope. Interspersed through the area arelimestone pavements and outcrops, coralreefs and shoals.The continental shelf is linked biologicallyto coastal areas through animal migrations.For example, many species of prawnsand demersal fish have a juvenile phasein coastal and estuarine habitats withsubsequent migration to inner and outershelf habitats. The components are alsolinked physically, with key large scaleprocesses including strong tidal currents,particularly in the coastal and inner shelfregion and cyclones which aid in mixingnutrients and transporting sedimentsacross the shelf.The continental slope and deep waterhabitats are also important, thoughtheir role in ecosystem dynamics is lesswell understood. Nevertheless, there islikely to be a link between upwelling ofnutrients onto the continental shelf andrich soft sediment seabed communitiesthere. The continental slope habitats alsoprovide for a range of relatively uniquedeep water specialists, including fish andmarine mammals such as beaked whales.
Coastal and Marine Natural Values of the Kimberley15.2.2 COASTAL MARINEHABITATSThe Kimberly coast is dissected into amosaic of different habitat types, largelydriven by local environmental conditions.Mangroves generally fringe the head ofbays and inlets that are sheltered fromwaves. Mangroves also extend inlandalong the edges of estuary tidal channels.Salt flats and marshes are present insome areas on the landward side ofthe mangrove fringe, particularly areasthat flood during the monsoon season.Seaward of the mangroves, there areoften mud flats, sand flats or sandybanks, depending on the current, waveexposure and sediment regime. Theshores exposed to wave action generallyhave sandy beaches, rocky reef orlimestone platforms.The high tidal range in the Kimberlycauses very strong currents, whichtransport sediments in the coastalregion, forming subtidal habitats suchas channels, harder sand banks andsoft muddy deposits further offshore(to approximately 20 m depth). Thecurrents also scour sediments from reefstructures and supply food to associatedfilter-feeding invertebrates. Seagrassgenerally occurs on sandy banks withits distribution greatly influenced bysubstratum stability and light climate(a function of sedimentation, turbidityand depth).Reefs and coral communities are scatteredthroughout the region, generally on theseaward, exposed coasts of the mainlandand fringing the islands. There are coralreefs present in between the islands. Thedistribution of coral habitat is not wellknown, but there may also be bands ofsubtidal coral communities along thecoast, as mapped for the Pilbara coast(although that region has a much reducedfluvial sediment input; Magvelashviliet al., 2006). Macroalgae communitiesoccur on hard substrata such as limestonereefs and platforms and, like seagrass,tends to occur in areas with a higher lightregime and reduced sedimentation.The coastal waters and associatedhabitats, typified by the high sedimentloadings, transport and mixing from tidalcurrents, generally extend onto the shelfto depths of 15-20 m. The high turbidityof the coastal waters is persistent, butthe suspended sediment concentrationvaries by an order of magnitude betweenspring and neap tides (Magvelashviliet al., 2006).
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coastal and marine natural values of the kimberley - wwf - Australia

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